The present invention relates to a fast atom bombardment source (FAB (Fast Atom Bombardment) or saddle field source) and a fast atom beam emission method for generating plasma to emit atoms, and a surface treatment apparatus (for example, surface modification apparatus) provided with the fast atom bombardment source.
An atom beam which has kinetic energy much larger than those of atoms and molecules existing in the atmosphere at room temperature and a directional property is called fast atom beam, and an apparatus which generates the fast atom beam is called fast atom bombardment source.
The fast atom bombardment source is mainly used for a processing step in a semiconductor device production process. The feature of the fast atom bombardment source is that a target to be processed is not charged unlike in the case of using an ion beam. Therefore, the fast atom bombardment source can be used even when the charge possibly damages the target or even when desired process accuracy cannot possibly be ensured by the charge depending on a characteristic of the target.
However, in the conventional fast atom bombardment source, there is an issue that density of the emitted atom beam is hardly equalized. In order to solve the issue, Japanese Examined Patent Publication No. 3363040 discloses a technique of equalizing a planar distribution of the atoms emitted from the fast atom bombardment source.
In a configuration of the fast atom bombardment source disclosed in Japanese Examined Patent Publication No. 3363040, an emission electrode or a gas introduction electrode which has a plurality of holes is provided in an electric-discharge vessel which generates the plasma, and lengths or diameters of the holes are set so as to differ from one another depending on their positions, whereby evenness of the distribution of the emitted atoms is achieved.
However, a distance between the atom bombardment source and the target sometimes becomes uneven depending on a shape of the target to be processed and the configuration of installation. Additionally, in the case where the target such as a wafer larger than a chip is processed, or in the case where an etching rate is enhanced, or in structure of equipment, the distance between the atom bombardment source and the target sometimes becomes uneven. In such cases, when the target is irradiated with the fast atoms, the density of the atoms impinging on the target is not equalized, and a structure of the target is not matched with design, which results in generation of a defect.
Furthermore, in the conventional technique, it is necessary to change the structure of the atom bombardment source when the amount of processing or target to be processed is changed, which increases cost.
In view of the foregoing, an object of the present invention is to provide a fast atom bombardment source, a fast atom beam emission method, and a surface modification apparatus which enable the desired emission atom density distribution per unit time to be inexpensively achieved in short time.